1. Field of the Invention
This invention relates to dye laser amplifiers.
2. Discussion of Prior Art
Dye lasers are a known type of laser in which a dye cell pumped with energy causes a laser action from the cell. The dye cell is a vessel containing a gaseous liquid or solid dye and is often arranged between reflectors forming a laser cavity. An advantage of dye lasers is that their frequency can be readily changed. For example one of the cavity reflectors may be a reflective grating. Varying the angle of this grating to the cavity varies the dye laser output frequency. Output power is a function of pumping power. The limit of output power is reached when the the pumping power is sufficient to cause a total population inversion the dye and the optical design of the laser allows all of the stored energy to be extracted from the dye. Large output powers may be achieved by increasing the size of the laser, but this is often not desirable. Instead a relatively lower power laser may be used and its output amplified.
Laser amplifiers are useful because they allow the maximum optical extraction to be achieved from a laser medium. A normal laser requires feedback in order to sustain the laser oscillations. The feedback is usually provided with partially reflective mirrors and it is only the transmitted portion of the beam that forms the laser beam that emerges from the device. No matter how low the reflectivity of the exit mirror becomes, the output beam can never be 100% since some portion is required to provide the feedback. A laser amplifier has no mirrors to provide a transmission loss, but instead relies on there being a laser beam present from another laser. Providing that this beam is intense enough, it can cause all of the amplifer energy to be extracted.
Laser amplifiers are also useful in other areas; for instance, if a high power laser is required to be built using some components which are sensitive to laser damage, then a low power laser can be designed and then amplified without affecting the original beam qualities. In this way the sensitive optical components are not exposed to damaging power levels.
There are many sorts of amplifiers that are currently used in conjunction with dye lasers but the two most used employ dye as the the gain medium. These amplifiers are flashlamp pumped and laser pumped. Additionally, laser pumping may be either transverse in geometry (pumping beams is at some angle, usually 90.degree., to the extracted dye laser beams) or longitudinal in geometry (pumping beam is coaxial to the extracted dye laser beams).
A disadvantage of using amplifiers is added system complexity, i.e. additional optics, dye cells and support mounts.
Both dye lasers and amplifiers are described for example in Dye Lasers, edited by F. P. Schaffer, second edition, published by Springer-Verlag, 1977.
One problem with existing amplifiers is that they amplify or broaden the bandwidth, i.e. the output consists of a wider range of frequencies Typically a single longitudinal mode (SLM) dye laser has a bandwidth of less than 1 GHz and after amplification it increases to much greater than 1 GHz. It is highly desirable to amplify the output of a dye laser and maintain a narrow bandwidth.
As used in this specification the term light includes electromagnetic radiation in the visible, infra red, ultra violet, and nearby wavelengths.